Lightning stroke generator



Jan. 7, 1941. L BELLASCHI 2,228,070

LIGHTNING STROKE GENERATOR Filed Oct. '7, 1959 2 Sheets-Sheet 1 WITNESSES: INVENTOR fQ%% Pefer Age/mm;

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ATTORN EY J 7., 1941- P. BELLASCHI 7 LIGHTNING STROKE GENERATOR Filed Oct. '7, 1959 2 Sheets-Sheet 2 INVENTOR P6237 LBeZ/ascfiz' Q4. M r

ATTORN EY WITNESSES:

Patented Jan. 7, 1941 UNITED STATES ucn'rumo s'raoxn cmvaaa'roa Peter L. Bellaachi, Sharon, Pa, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsyl- Vania Application October "I, 1939, Serial No. 298,445

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This invention relates to lightning stroke generators, and particularly to such generators in which are combined a lightning stroke voltage generating apparatus and a lightning stroke current generating apparatus.

Prior to my invention disclosed and claimed in Patent No. 2,032,904, issued March 3, 1936, socalled lightning generators which were utilized for testing the insulation of electrical apparatus were high-voltage impulse generators capable of developing a very high voltage with very little current. In order to provide an electric discharge that more nearly simulates a stroke of lightnin it was necessary to provide for a heavy current discharge starting during the occurrence of the voltage impulse wave and following for a much longer time than the voltage impulse wave. In my patent above referred to, I provide equipment designed to apply current strokes to apparatus under test which would more nearly simulate the destructive forces or heavy lightning currents than did existing apparatus of this character previously employed. Since the time of making the invention covered in my prior patent, however, experimental data has been obtained establishin with greater detail than was at that time known the nature of a lightning stroke discharge, particularly in that the current discharge, in addition to its initial high current wave, may have a relatively long sustained discharge lasting for several times the duration of the high current wave, which is of importance because, due to its time of duration, it may represent a considerably greater dissipation of energy than does the initial high current wave. This sustained current discharge has been shown to be the cause of the fusing of metal parts, or the ignition and burning of combustible material.

Lightning stroke discharges may take several forms. A typical stroke may, consist of three characteristic elements-a very high voltage wave of very short time duration, a high current wave of longer duration, and a sustained current flow of moderate value having a much longer time duration. The first, or voltage impulse, may develop to a value of many millions of volts reaching its crest value in. about 1 microsecond, the total wave lasting for a duration of time of the order of 2 to 4 microseconds. The second element, or initial current surge, may rise to a crest value of from several thousand amperes to 200,000 amperes from 5 to 10 microseconds, reducing to one-half the crest value in from 50 to 200 microseconds, 100 microseconds being typical. The third characteristic element of the stroke, or sustained discharge, may be of the order of 100 to 5000 amperes, continuing from 1000 microseconds to 10,000 to 100,000 microseconds. Any one of the two current elements of the/discharge may at times occur alone, or they may both occur in the same discharge in various amounts or degrees.

Observations and experiments have shown that the characteristic eflect of the first, or high-voltage discharge, is to puncture insulating material of high dielectric value; the characteristic eiiect oi the second element or high current impulse, is the shattering or splintering of objects affected thereby; and the characteristic eflect oi the third, or sustained current discharge, is that of burning, melting or igniting the objects to which it is applied. It has been shown, for example, that a high current wave of 100 microseconds duration, which will splinter strong dielectric material and hurl the parts with great violence in all directions, cannot be made to lgnite even readily inflammable material, such as cloth or excelsior, or to damage electrical conducting metals, while the third, or sustained discharge oi from 100 to 5000 amperes for a duration of 1000 microseconds or longer, will both burn or ignite combustible materials, and will melt or fuse large voids in solid electrical conducting metal objects. This third characteristic element of the typical lightning stroke is somewhat similar, in effect, to short-circuit power currents of great current values lasting for from one-halt cycle to several cycles duration, or to a direct-current flow of equal energy dissipation. Not all lightning strokes have all three characteristic elements. They may have the first, or impulse voltage element, with either the high current wave of short duration or the sustained current wave of longer duration, or both, or there may be a current wave of irregular characteristic following a voltage discharge, which wave may .have several high current peaks 0! short duration with comparatively low current values between them.

Another characteristic of the lightning stroke discharge is the repetition of several strokes in close succession. Such strokes usually each start with an impulse voltage wave and may be followed by current discharges of the character pointed out above.

It is an object of my invention to provide a lightning stroke current generator of a type that will produce a relatively long sustained current discharge that is characteristic of the burning or heating portion of a typical lightning stroke.

It is a further object of the invention to provide a lightning stroke generator of the type above indicated for delivering a high-voltage surge discharge, a relatively high current surge discharge of relatively short duration, and a relatively low current discharge of relatively long duration.

It is a further object of my invention to provide a lightning stroke generator for developing a plurality or series of lightning stroke discharges in quick succession.

Referring to the drawings:

Figure 1 is a diagrammatic view of apparatus and circuits for producing a lightning current discharge of long duration;

Fig. 2 is a diagrammatic view of apparatus for combining the initial high-voltage and high current discharge with the sustained moderate current discharge of long duration;

Fig. 3 is a diagrammatic view of another embodiment of apparatus for producing a lightning current discharge of long duration combined with the lightning discharge of shorter duration;

Fig. 4 is a diagrammatic view of circuits and apparatus for effecting a series of lightning strokes in quick succession;

Fig. 5 is a view of the tripping switch for controlling the sequential discharge of the lightning stroke generators illustrated in Fig. 4; and

Fig. 6 is a diagrammatic veiw of another embodiment of apparatus for developing a multiple stroke discharge.

Referring to Fig. 1 of the drawings, a voltage impulse generator I is illustrated in combination with apparatus including a transformer 2 for developing a sustained current discharge of moderate value for several thousand microseconds. The transformer 2 is provided with a high-voltage winding 1 and a low-voltage winding 8, and is connected by a circuit controlling device 9 to a source of alternating current represented by the circuit conductors i2. The device 9 may be a mechanical switch, or it may be other suitable apparatus, such as an ignitron timer, well known in the art for permitting current flow for a selected duration of a half-cycle or more. The winding 1 is connected between terminal conductors 4 and 5 of the test-piece 3 under test, the circuit including a de-ion gap l3 and a spark gap i4. The de-ion gap l3 consists of a fusible wire i5 within a tube iii of insulating material, such as fibre, or other equivalent material.

The high-voltage impulse generator I consists of a plurality of capacitors I! connected to discharge in series through a plurality of sphere gaps i8, establishing a high voltage between ground at 2i and the sphere gaps I9, which voltage is applied across the test-piece 3 to ground at 6 and across a high ohmic resistor 22 connected in parallel therewith. The condensers i! are connected to be charged in parallel from conductors 23 and 24 through individually associated resistors 25 and 26 from a source of energy, represented generally at 21, and including an alternating-current transformer 28 having a highvoltage winding supplying two rectifiers 3| and 32 connected in circuit with electrical storage devices, such as capacitors 33 and 34, to the midpoint of which the high-voltage transformer winding is connected through a resistor 35, and to the outside terminals of which the rectifiers 1i and 32 are connected.

A gap device, including spheres 25, 21 and 38, is provided for initiating the discharge of the voltage impulse generator 3!, the two elements 35 and 31 being connected respectively to adjacent capacitors IT. The intermediate sphere II is connected to a tripping and synchronizing circuit for determining the exact moment of discharge with respect to the alternating current supplied 5 to the conductors l2, so that the discharge occurs at the desired part of the alternating-current wave.

A simplified tripping and synchronizing circuit for this purpose is illustrated as comprising a 10 push button for closing a circuit to energize a step-up transformer 4i, one output terminal of which is connected to the middle electrode 42 of a triple gap device 42, the two outer terminals 44 and 45 of which are connected to the other termil5 nal of the other output terminal of the step-up transformer 4| through a resistor 48 and a capacitor 41, respectively, so that the triple gap device 42 breaks down at or near the crest of the voltage wave of the transformer 4i. The terminal elec- 20 trode 44 is connected by conductor 48 to the intermediate sphere 38 of the main triple gap device 39, the connections being such that the intermediate gap electrode 38 is thus given a potential which is opposite to the potential of the ungrounded electrode 21 of the main gap device, so that the gap between the spheres 31 and 38 first breaks down, after which the full voltage of the lower condenser I1 is applied to the gap between the spheres 36 and 28, causing it to break down. so The flow of current through the gap device 39 so modifies the potentials across the succeeding gaps I I of the impulse generator as to cause the entire series of gaps to break down and apply the entire series voltage of the several capacitors ll 35 to the gap l9, which in turn breaks down applying the high-voltage impulse to the test-piece 3.

The discharge of the high-voltage impulse generator l causes the gap I4 to break down and connect the transformer 2 to the test-piece 3 40 through the de-ion gap l3. The timing of the discharge of the voltage impulse generator may be such as to occur during the early portion of a half-cycle output from the transformer 2. It will be noted that a half-cycle at 60-cycle fre- 45 quency has a duration of 8333 microseconds. Thus the number of half-cycles is controlled to attain the desired duration. The interruption of the sustained current wave from the transformer 2 may be effected either by the setting of the 50 fused de-ion gap l3 or by the operation of the circuit breaker I! on the low-voltage side of the transformer. Tests have been made with the equipment disclosed in Fig. 1, with varying amount of current and duration of wave thus showing that the same amount and nature of fusion of metal objects can be produced as those observed from natural lightning, the equipment simulating the long sustained current discharges of lightning causing such heating or burning of the materials.

Fig. 2 discloses a lightning stroke generator combining the voltage impulse generator i and the long sustained current generator 2 with a current impulse generator 5| corresponding to that disclosed in my Patent No. 2,032,904, and comprising a plurality of capacitors 52 connected in parallel between terminal buses 53 and 54 that are connected across the test-piece 3 through an impedance device 55 upon the breakdown of gap 56, which occurs upon the discharge of the voltage impulse generator I. The device 55 comprises a high resistance fusible link 51 within an insulating tube 58 of fibre or other equivalent material. The device 55, which appears in the diagram 7 to be similar to the device I! and resembles it structurally, performs a diflerent tunction from the device II, and for that purpose the fusible link is of high resistance 01' the order 01 one to several hundred ohms, so as to prevent enough oi the impulse voltage discharge from entering the current generator ii to produce a voltage suillcient to break down the insulation of the testpieoe 9. The (use link 51, after 1 or 2 microseconds, converts into a low resistance are, so that the discharge of the current generator follows immediately after the high-voltage discharge through or across the test-piece 3. Also, the flber tube 99 serves to interrupt the current after the high current discharge and segregate the current generator 5| from the test object I.

The lightning stroke generator diagrammatically illustrated in Fig. 2 will supply an initial high-voltage surge from the generator I, causing the spark gaps between the spheres 56 and M to break down to supply respectively an initial high current impulse surge from the generator I and a sustained current surge of lesser current value, but of longer time duration from the current generator 2, to simulate the three element characteristic of a lightning stroke described above.

Fig. 3 illustrates a lightning stroke generator for developing the same three-element characteristic discharge including the voltage impulse generator I, the impulse generator 5|, and an impulse generator Bl, which may be similar in gen. eral nature'to the generator 5i and consisting 01 a plurality of capacitors 62, 63, 64 and 65 connected to bus terminals 99 and 61 for applying a current surge across the test-piece 3 upon the breakdown of the gap between spheres G9, which occurs upon the discharge oi. the voltage impulse generator in the manner above described. The impulse generator 9| discharges through an impedance or resistor device 69 that is of a value sumcient to limit the discharge current to the moderate value'typlrled by the sustained discharge of a lightning stroke as described above. The capacity or the generator Bl must be sufflcient to supply the desired discharge current for the time necessary to simulate such sustained discharge. It will be appreciated that in the several surge generators I, II and 6| the number 01' capacitors actually used will be much greater than those shown to diagrammatically illustrate such generators. It will also be appreciated that where it is desired to apply the discharge from any of the several current generators 2, 5| or iii, the tripping circuit shown in Fig. 1, employing a middle terminal 39, may be applied to any of the gaps between spheres ll, 56 or 69. Thus any one of the three characteristic elements of the lightning surge pointed out above may be apso plied separately to the test-piece, if desired.

Fig. 4 illustrates a lightning stroke generator capable of supplying repeated impulses in rapid succession. It consists of a plurality of lightning stroke generators II, 12, I3 and 14, which are 65 here illustrated as each corresponding in nature to the voltage impulse generator I shown in Figs. 1, 2 and 3. For the purpose of simplicity,

only the voltage impulse generators are shown,

although it will be appreciated that there may 70 be associated with each of the voltage impulse generators any of the combinations of current impulse generators shown in Figs. 1, 2 and 3, or any of the current impulse generators may be used alone to provide a series of repeated current impulses without the use of the voltage impulse generators, if desired. The sequential operation of the several voltage 'generators is controlled by a rotating disc I6 operated by a motor I9, as shown in Fig. 5, and carrying thereon a sphere 11 which, as it rotates, comes between a pair of spheres 19 and 19 to partially bridge the gap therebetween and cause the discharge of initiating condensers ll, l2, l9 and 94 to thus secure the proper interval of time between the'discharge oi the successive lightning stroke generators. Thus each of the generators may be designed to have suitable voltage and current characteristics at a discharge in proper sequence to simulate the multiple stroke discharge of certain types of lightning strokes.

Fig. 6 shows other apparatus for producing a multiple stroke discharge. A large power transformer 9| is provided, receiving energy from supply conductors 92 and 99 as controlled by a switch 9|. The transformer supplies charging current to a large high-voltage capacitor 95 during a halt-cycle or several halt-cycles output of the same polarity from transformer 9|, which is effected by the proper operation of the switch 9|. As the switch 94 receives a full voltage charge, the gap between spheres 99 breaks down, d scharging to ground at 91, and applying the discharge voltage across the test-piece 3. By suitable control of the switch 94, the number and sequence oi! condenser discharges is adjusted as desired. A de-ion gap device 99 may be provided in the circuit for interrupting the circuit through the gap between spheres 96. In Fig. 6, a transformer 99 is shown for applying power voltage excitation to the test-piece I, so that the impulse test may be made with full power excitation applied thereto in accordance with the method of testing described in United States Patent 1,957,306, issued to F. J. Vogel on May 1, 1934, and assigned to the same assignee as this application. It will also be appreciated that the apparatus disclosed in Figs. 1 to 4 may be used with the application of dynamic power across the insulating material during the discharge of the lightning stroke generator through or across the material or test-piece 9 being tested.

It will be apparent to those skilled in the art that many modifications oi! the apparatus and circuits illustrated may be made within the spirit of my invention, and I do not .wish to be limited otherwise than by the scope of the appended claims.

I claim as my invention:

1. A combined lightning-stroke current and voltage generator comprising an impulse voltage generator including a plurality of capacitors connected to discharge in series, an impulse current generator having a low-impedance, high-current discharge characteristic for delivering a large currentior a short duration of time including a plurality of capacitors and buses for connecting said capacitors in parallel, an impulse current generator having a high-impedance, lowcurrent discharge for delivering a relatively lower current for a relatively longer time comprising a plurality of capacitors, buses connecting said capacitors in parallel, and an impedance device in circuit with said buses for limiting the rate of discharge thereof, terminal connections for a test-piece, means for controlling the connection of said terminal connections to said impulse voltage generator, and means responsive to the discharge of said impulse voltage for connecting said impulse current generators to said terminal connections.

2. A combined lightning current and voltage generator comprising an impulse voltage generator including a plurality of capacitors connected to discharge in series, an impulse current generator having a low-impedance high-current discharge characteristic for delivering a large current for a relatively short duration of time comprising a plurality of capacitors and buses connecting said capacitors in parallel, means for delivering a current discharge of relatively lower current value for a relatively longer time, terminal connections for a test piece, means for controlling the connection of said terminal connections to said impulse voltage generator, and means responsive to the discharge of said impulse voltage generator for effecting the discharge of said two current discharge devices.

3. A combined lightning-stroke current and voltage generator comprising an impulse voltage generator including aplurality or capacitors connected to discharge in series, capable of delivering a discharge voltage wave rising to several million Volts in 1 microsecond, an impulse current generator characterized by suflicient capacity to give a maximum crest value of discharge of the order of 100,000 amperes and capable of sustaining the current flow above one half its crest value for 100 microseconds, an impulse current generator having suflicient capacity to deliver a discharge current 01' the order of 5,000 amperes for a duration of several thousand microseconds, terminal connections for a test piece, means for controlling the connection 01' said terminal connections to said impulse voltage generator, and means responsive to the discharge of said impulse voltage for connecting said impulse current generators to said terminal connections.

4. A combined lightning current and voltage generator comprising an impulse voltage generator including a plurality of capacitors connected to discharge in series, an impulse current generator having a low-impedance high-current discharge characteristic having sufiicient capacity for delivering a current wave having a crest value of the order 01' 100,000 amperes and capable of sustaining the current flow above one half its crest value for a time of the order oi from '2000 to 7000 microseconds, means for delivering a current of the order oi 5000 amperes for a duration from three thousand to five thousand microseconds, terminal connections for a test piece, means for controlling the connection of said terminal connections to said impulse voltage generator, and means responsive to the discharge of said impulse voltage for connecting said impulse current generators to said terminal connections.

5. A combined lightning-stroke current and voltage generator comprising an impulse voltage generator including a plurality of capacitors connected to be discharged in series, an impulse current generator having a high-impedance lowcurrent discharge for delivering a discharge current for a duration of several thousand microseconds comprising a plurality of capacitors,

buses connecting said capacitors in parallel, and an impedance device in circuit with said buses for limiting the discharge thereof, terminal connections for a test piece, gap means for controlling the connection of said terminal connections to said impulse voltage generator, and means responsive to the discharge of said impulse voltage generator for connecting said current generator to said terminal connections.

6. A combined lightning-stroke current and voltage generator comprising an impulse voltage generator including a plurality of capacitors connected to be discharged in series, means for delivering a current discharge of the order of 2000 amperes to 5000 amperes for a duration of the order of from 2000 microseconds to 7000 microseconds, terminal connections for a test piece, gap means for controlling the connection 01' said terminal connections to said impulse voltage generator, and means responsive to the discharge of said impulse voltage generator for connecting said current generator to said terminal connections.

7. A combined lightning-stroke current and voltage generator comprising an impulse voltage generator including a plurality of serially connected capacitors, an impulse current generator including a plurality of capacitors connected in parallel and an impedance device for limiting the current flow therefrom to the order of 5000 amperes, the capacitors having sufllcient capacity to deliver a discharge current of that order for a duration or several thousand microseconds, terminal connections for a test piece, means for controlling the connection or said terminal con- 3 nections to said impulse voltage generator, and means responsive to the discharge of said impulse voltage generator for connecting said impulse current generator to said terminal connections.

8. A lightning-stroke generator comprising a plurality of impulse voltage generators each comprising a plurality oi'.capacitors connected to discharge in series, terminal connections for a test piece, means for controlling the connection of said terminal connections to said several impulse voltage generators in predetermined sequence and at predetermined spaced time intervals.

9. Apparatus comprising a plurality of lightning-stroke generators each including an impulse voltage generator having a plurality of capacitors connected to discharge in series, an impulse current generator having a low-impedance highcurrent discharge characteristic for delivering a current of the order of 100,000 amperes for a duration of from 40 to 200 microseconds, and means for delivering a current discharge oi the order of 5000 amperes for a duration of several thousand microseconds, terminal connections for a test piece, means including spark gaps for controlling the connection of said terminal connections to several lightning-stroke generators in a predetermined sequence at predetermined short time intervals.

PETER L BELLASCHI. 

